Ground Penetrating Radar (GPR)
A GPR is like an ultrasound scan of the ground: it looks under the surface without digging. An antenna pulled by hand or mounted on a vehicle produces a vertical cross-section of the subsurface, revealing pipes, voids and different soil layers.
How it works
- Emission: the antenna sends electromagnetic pulses down into the ground, at regular intervals, while the cart moves forward.
- Reflection: whenever a pulse meets something different from the surrounding material — a pipe, a void, a rock — part of the wave bounces back and is captured by the receiver.
- Depth: the longer the echo takes to return, the deeper the object is. The wave speed depends on the material: roughly v ≈ c / √εr, where c is the speed of light and εr is the dielectric constant of the ground.
- Radargram: one trace per measurement position; put side by side, they form the final image (B-scan). An isolated object draws a hyperbola whose apex sits exactly above it: the curve arises because the time of flight grows as the antenna moves away.
Note
The upper panel of the animation is the radargram: the moving cursor is the antenna position, and the hyperbolas appear as the radar detects the buried objects.
Depth or detail?
The antenna frequency defines the trade-off of every survey:
- Low frequency (100–400 MHz): reaches depth (several metres), but shows little detail.
- High frequency (900–2000 MHz): reaches only a few decimetres, but reveals fine details such as rebars and cracks in concrete.
The ground matters too: conductive materials such as clays and saline soils absorb the wave and reduce the penetration range.
What it is used for
- Locating pipes and ducts underground.
- Inspecting concrete pavements and slabs.
- Assessing the condition of roads and railways.
- Studying stratigraphy and archaeology, as well as snow and ice.
In my work I develop the software that processes this radar data, up to the application of Explainable AI techniques to help its interpretation.